Polymorphisms of selected genes coding for antigens of theileria parva circulating in cattle in Southwestern Uganda

Abstract

Theileria parva is a tick-borne apicomplexan haemoprotozoan parasite of cattle which is by far the most pathogenic and economically significant Theileria species in Eastern, Central and Southern Africa. It causes an acute and often fatal disease in cattle called East Coast fever (ECF). Current control strategies of the disease include regular tick control by use of acaricides or treatment of sick animals, both of which have proved inadequate. The only vaccination control method is the Infection and Treatment Method (ITM) using the Muguga cocktail but its success requires cross-protection against all known field strains. The parasite strains in Uganda have not been fully characterized to ensure cross-protection against the parasite antigenic diversity expressed at the schizont stage in cattle and buffalo (the pathogen‟s wild reservoir). Consequently, this study was carried out to investigate the polymorphisms at three important T. parva antigen gene loci; p104, p67 and PIM. Two hundred fifty (250) cattle blood samples (Ankole long-horn) from Kiruhura district (Southwestern Uganda) were screened for Theileria parva infection by nested PCR for the p104 antigen gene. Fifty (50) infected samples were identified and subsequently analysed for allelic diversity at the p104 and PIM loci using PCR-RFLP; and DNA multi- sequence alignment for the p67 locus. Consequently, p104 gene analysis predicted two alleles, one of which occurred in 13/17 (82%) of the samples analyzed. The PIM gene demonstrated up to 11 alleles and occurrence of multiple T. parva infections in 20/22 (91%) of the samples analysed. None of the p104 and PIM gel profiles (alleles) was identical to similar analysis of the T. parva Muguga isolate (Sibeko et al., 2011). The p67 gene sequences generated were identical to those of the reference T. parva Muguga and T. parva Katete isolates. Findings in this study predict a diverse population of Theileria parva in Kiruhura with respect to the p104 and PIM antigen genes. Some alleles of the p104 and PIM genes occur more frequently among field isolates and could represent the dominant strains of the parasite. Field variants of T. parva that are distinct from T. parva Muguga strain with respect to the p104 and PIM genes occur. Similar studies should be generated from the different agro-ecological zones of Uganda to identify dominant parasite strains in T. parva populations for inclusion in the vaccine cocktail to improve cross protection of the local cattle population against parasite heterologous challenges. 1